The troubled singer - who was booed during a shambolic European comeback performance on Saturday night (18.06.11) in Belgrade - has reportedly been retired "indefinitely" by her manager Raye Cosbert so she can concentrate on her health and well-being.

A source close to Amy - who checked out of rehab three weeks ago after being treated for drink problems, and has battled drug addiction in the past - told The Sun newspaper: "It has been hard for Raye to watch her get into trouble over the years. There's only so much he can do - but enough's enough.

"She's going away and this time it could be for years."

Amy has so far cancelled the next two shows of her 12 date tour - in Greece and Turkey - but the source said Raye is likely to make her cancel all of the shows and head back to rehab.

Following the 'Back to Black' hitmaker's Serbian show - in which she looked wild-eyed and confused, missed her cues, slurred her words and even threw one of shoes into the crowd - the star will not take her fee, so disgruntled fans may get their money back, even though she is entitled to payment.

A promoter told the Metro newspaper: "She did it all according to the agreement. She arrived in Belgrade on time and stayed on stage for 70 minutes, so we can't do anything."

However, Amy agreed her performance was below par and will not take any money for the show.

Another source added: "The fact is that Amy won't be taking her payment for the gig."